Did someone mention "are you sure" the valves are actually opening and closing AKA something wrong in the valve train HOLDING the valves OPEN or cam so flat they really aren't opening, etc........Does it have oil blowby, indicating poor ring seal?
You have FOUND the area of trouble.........very poor compression. Use air/ leak test to try and find WHERE the compression is escaping. Apply air into the cylinder at TDC and listed "to where" it is coming out.......oil filler, exhaust, carb, and radiator